There is known an on-demand type inkjet recording system for ejecting ink droplets from nozzles according to an image signal and forming an image with the ink droplets on a recording paper. The on-demand type inkjet recording system mainly includes a heat generating element type head and a piezoelectric element type head. The heat generating element type head is constituted to energize a heat generating element provided in an ink channel to generate air bubbles in ink and eject the ink pushed by the air bubbles from nozzles. The piezoelectric element type head is constituted to eject ink stored in an ink chamber from nozzles by utilizing deformation of a piezoelectric element.
The piezoelectric element converts a voltage into force. When an electric field is applied to the piezoelectric element, the piezoelectric element causes extension or shear deformation. As a representative piezoelectric element, a lead-zirconate-titanate is used.
As an inkjet head that utilizes the piezoelectric element, a constitution including a nozzle board formed of a piezoelectric material is known. In this inkjet head, electrodes are formed on both surfaces of the piezoelectric nozzle board to surround nozzles that eject ink. The ink enters between the nozzle board and a substrate that supports the nozzle board. The ink forms meniscuses in the nozzles and is maintained in the nozzles. If a high frequency voltage is applied to the electrodes, the nozzle board is oscillated and oscillation energy is radiated from the circumferential edge of the nozzle toward the center thereof. The oscillation energy is concentrated to the center of the nozzle and thus energy is generated in the direction normal to the surface of the ink, resulting in jetting an ink droplet from the nozzle.